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Two complementary experimental programs have taken place to investigate the origin and evolution of shape coexistence in the light mercury region. Recoil Distance Doppler-shift measurements were performed at the University of Jyvaskyla utilizing the Koln plunger device in conjunction with the JUROGAM + RITU + GREAT setup. In addition, Coulomb excitation measurements of 184,186,188Hg were performed at REX-ISOLDE using the MINIBALL Ge-detector array. The results of the lifetime measurements of the yrast states up to I^{\pi} = 10+ in 182Hg are reported. Preliminary analysis of the Coulomb excitation data is also discussed. ispartof: pages:414-418 ispartof: AIP Conference Proceedings vol:1090 pages:414-418 ispartof: Capture gamma-ray spectroscopy and related topics location:Koln, Germany date:25 Aug - 28 Aug 2008 status: published

Neutron capture gamma rays were measured for all stable Se isotopes in an incident neutron energy region from 15 to 100 keV. A neutron time‐of‐flight method was adopted with a ns‐pulsed neutron source based on the 7Li(p,n)7Be reaction and with a large anti‐Compton NaI(Tl) spectrometer. A pulse‐height weighting technique was applied to the observed capture gamma‐ray pulse‐height spectra to obtain the capture yields. Using the standard capture cross sections of 197Au, the capture cross sections of stable Se isotopes were derived with an error of about 5%. The capture gamma‐ray spectra were obtained by unfolding the observed capture gamma‐ray pulse‐height spectra. The present results for the capture cross sections are compared with the previous measurements and the evaluations of JENDL‐3.3 and ENDF/B‐VI.8 and VII.0.

An essential property of collectivity is the proton‐neutron degree of freedom, that leads to the so‐called states of mixed symmetry. Predictions for the electromagnetic decay of the lowest‐lying mixed‐symmetry state 2MS,1+ in vibrator‐like even‐A nuclei are a strong M1 decay to the fully‐symmetric 21+ state and a weak collective E2 decay to the ground state 01+. Excited states in 62Zn have been studied via the 61Ni(3He,2nγ) reaction using the HORUS‐cube spectrometer of the Institute for Nuclear Physics in Cologne. Two fragments of the mixed‐symmetry state 2MS,1+ could be identified by determining absolute M1 transition strengths to the 21+ state.

The N = 52 nucleus 98Pd was investigated at the Cologne TANDEM accelerator both with the Cologne plunger using the recoil distance Doppler‐shift method (RDDS) and with the Cologne HORUS spectrometer for a γγ angular correlation experiment. For the first time lifetimes of yrast states and highly excited low‐spin states were measured in 98Pd and the low‐spin level scheme was extended. From our data we were able to interpret 98Pd as a nucleus that exhibits some collective features, but is obviously much less collective than the neighboring N = 52 isotones 94Mo and 96Ru due to its closeness to doubly‐magic 100Sn.

In recent years collectivity in the mass region around A = 100 has become the focus of increased interest. The N = 52 isotones were investigated in detail and phonon excitations ‐especially one‐ and two‐phonon mixed‐symmetry states—were identified. In order to investigate how vibrator‐like behavior and states with mixed‐symmetry character evolve with increasing neutron number it is interesting to study the N = 54 isotones. Therefore an experiment to measure the low‐spin excitations of 100Pd was performed at the FN‐Tandem accelerator with the HORUS cube spectrometer. Besides the determination of excitation and transition energies and branching ratios, spins and multipole mixing ratios resulted from the γγ angular correlation analysis. The newly gained data were compared with predictions from theory both from collective models and from shell model.

A RISING experiment with an aim to study exotic Cd nuclei was carried out at GSI‐FRS facility. Some preliminary results from this experiment are presented here. In particular, the β decay of 96Cd to 96Ag revealed the existence of a high spin isomer predicted a few decades ago. In this context, the structures of both these nuclei are discussed. Shell model calculations using the Gross‐Frenkel interaction are used to interpret the results.

Rational relations in values of stable intervals in near‐magic nuclei with Z = 26–29 confirm the presence of tuning effect in nuclear data.

The cross sections of 113In(α,γ)117Sb and 113In(α,n)116Sb reactions have been measured using the activation method. The experiments were carried out at the ATOMKI cyclotron accelerator in the center of mass energy range from 8.7 to 13.7 MeV. Astrophysical S‐factors have been calculated, and preliminary results are compared with statistical model predictions.

Although an important effort has been devoted in the last decades to measure reaction cross sections of interest in astrophysics, most nuclear astrophysics applications still require the use of theoretical predictions to estimate experimentally unknown rates. The nuclear ingredients to the reaction model should preferably be estimated from microscopic or semi‐microscopic global predictions based on sound and reliable nuclear models which, in turn, can compete with more phenomenological highly‐parametrized models in the reproduction of experimental data. The latest developments made in deriving the nuclear inputs of relevance in astrophysics applications are reviewed. They mainly concern nuclear structure properties, nuclear level densities, optical potentials.New developments to improve the predictions of radiative neutron capture rates are also discussed. They include the recent improvements made to the TALYS reaction code and the analysis of the pre‐equilibrium contribution. The direct reaction mechanis...

A method by Peres is used to draw spectra of the geometric collective model and the interacting boson model as lattices in the plane of energy versus an arbitrary observable average (or dispersion). Ordered (disordered) lattices are signatures of regular (chaotic) dynamics on both quantum and classical levels. The method enables one to disclose important features of the system.

It is shown that the assumption of a common mass coefficient for the three basic excitation modes contradicts in the case of the well deformed nuclei and for the usual one parameter quadrupole operator the experimental data on the energies and the E2 transition probabilities. It is shown also that it is possible to perform a transformation of the collective coordinates in such a way as to obtain the Hamiltonian with one common mass coefficient only, however, with the modified E2 transition operator with three parameters and the potential energy.

This paper presents a summary of the latest results from experiments performed at the Oslo Cyclotron. The Oslo group has developed a technique to extract simultaneously the level density and radiative strength function from primary γ‐ray spectra. A small (pygmy) resonance in the radiative strength function has been observed at around 3 MeV in several deformed rare earth nuclei. This resonance is shown to be of M1 character and the origin is thought to be the scissors mode. This resonance vanishes for the spherical Sm nuclei, as expected, since the scissors mode is dependent on deformation. Experiments performed in Oslo found the resonance in Dy isotopes to be twice as wide as the width extracted in an indirect way by comparing simulations with two‐step cascade spectra from neutron capture experiments. In 116,117Sn an increase in the slope of the radiative strength function around Eγ = 4.5 MeV indicates the onset of resonance‐like structures in both nuclei, resulting in a significant enhancement of the rad...

In the no‐core shell model (NCSM) framework, we calculate the 3He electric dipole moment (EDM) generated by parity‐ and time‐reversal violation in the nucleon‐nucleon interaction. While the results are somehow sensitive to the interaction model chosen for the strong two‐ and three‐body interactions, we demonstrate the pion‐exchange dominance to the EDM of 3He, if the coupling constants for π, ρ and ω‐exchanges are of comparable magnitude, as expected. Finally, our results suggest that a measurement of 3He EDM would be complementary to the currently planned neutron and deuteron experiments, and would constitute a powerful constraint to the models of the pion P‐ and T‐violating interactions.

High‐sensitivity studies of E1 and M1 excitations observed in the 138Ba(γ,γ′) reaction at energies below the neutron emission threshold have been performed. The electric dipole character of the so‐called “pygmy” mode was experimentally verified for excitations from 4.0–8.6 MeV. The fine structure of the M1 “spin‐flip” mode was observed for the first time in N = 82 nuclei.

Systematic cross section measurements of alpha‐capture reactions at sub‐Coulomb energies relevant to the p process were performed in the Ge‐Sn region. At the same time a recent global α‐nucleus optical model potential (OMP) based on the double‐folding method was updated using all existing data on alpha elastic scattering and alpha‐induced reactions. In this paper, we report on our recent measurements of alpha‐capture reactions and present calculations using the improved alpha‐nucleus OMP.

Excited states in 124Xe have been studied via the 12C(124Xe,124Xe*) Coulomb excitation reaction. Relative cross‐sections have been determined from the γ‐ray yields observed with Gammasphere. The E2 strengths between the low‐spin states in 124Xe have been determined. The results clearly show the realization of the O(5) symmetry even for the off‐yrast states with high τ, while the O(6) symmetry seems to be already broken.

Understanding the nuclear structure of 152Sm, along with other N = 90 isotones, has long posed a challenge. A rapid transition in shape between the spherical N = 88 150Sm and well‐deformed N = 92 154Sm is observed, along with strong evidence for shape coexistence. Competing ideas have been put forward over the decades, with the most recent being that N = 90 is at the critical point of a shape phase transition. Until recently, the lack of high‐precision data has not allowed the competing models to be extensively tested. In a coordinated program of investigation, a series of complementary experiments, which include high‐statistics β decay, multi‐step Coulomb excitation, the 150Nd(α,2n) reaction, and the (n,n′γ) reaction, have been performed for 152Sm. These experiments have revealed the existence of a pairing‐isomer band, a hexadecapole band, the lack of multi‐phonon β vibrational bands, and the repetition of structures built on the first excited Kπ = 0+ as built on the ground state. The status of these coo...

We are developing a new method to identify nuclear levels based on neutron capture reactions, named “TELLA‐2.” Measured data of prompt gamma rays from 33S(n,γ)34S was used to improve the method. We will show how we obtain candidates of nuclear levels.

We report on systematic investigations of low‐lying electric dipole (E1) strength in atomic nuclei. Using the method of real photon scattering the dipole response of all stable N = 82 isotones has been measured with high resolution. In all cases a resonance like structure of E1 strength is observed in the energy region 5–8 MeV, which shows a strong fragmentation. The total integrated strength increases towards the proton poorer isotones, indicating a dependence of the total strength on the neutron‐to‐proton ratio. The experimental results are compared to microscopic calculations within the Quasi‐particle Phonon Model (QPM). By including complex configurations of up to three phonons the calculation is able to reproduce also the fragmentation of the E1 strength and is in good agreement with the experimental observation.

It has been shown that the (3He,t) charge exchange reaction at intermediate energies, used at zero momentum transfer in combination with high‐resolution magnetic spectrometers is a very powerful probe for Gamow‐Teller strengths. Several N = Z nuclei such as 46V [1] or 50Mn [2] have been investigated. Recently ab‐initio nuclear structure calculations have become possible for light nuclei. Thus experimental studies on light nuclei have become of great current interest [3]. We review previous results obtained in 11C with respect to nuclear structure aspects and the Hoyle state, and present some early results of a 9Be(3He,t)9B experiment carried out recently, pointing out the significance of high‐resolution charge‐exchange reactions and the investigation of Gamow‐Teller strengths for the understanding of nuclear structure in light nuclei.

Low‐lying collective states in 136Ba were investigated with (n,n′γ) techniques, including Doppler‐shift attenuation lifetime measurements. The level spins, lifetimes, branching ratios, multipole‐mixing ratios and transition strengths reveal candidates for symmetric‐phonon states up to third order. The 2ms+ mixed‐symmetry state was confirmed as unfragmented and a candidate for a [21+⊗2ms+]3+ two‐phonon mixed‐symmetry state is proposed.

The rate of the 17F(p,γ)18Ne reaction is of significant importance in astrophysical events like novae and x‐ray bursts. A 3+ state in 18Ne predicted to dominate the rate was found at 599.8 keV using the 17F(p,p)17F reaction [1], but the resonance strength was unknown. For the first time, the 17F(p,γ)18Ne reaction has been measured directly with the Daresbury Recoil Separator, using a mixed beam of radioactive 17F and stable 17O from the HRIBF at ORNL. A γ width was found for the 599.8 keV resonance in 18Ne, and an upper limit on the direct capture S factor was determined at an intermediate energy of 800 keV.

International audience; The transient field strength for 76Ge ions, passing through iron and gadolinium layers at velocities ~Zv0, has been measured. Although a sizeable value has been obtained for Gd, a vanishing strength has been observed in Fe.

Resonances in the 12C(16O,γ)28Si radiative capture process at energies around the Coulomb barrier have been probed using the very selective 0° Dragon spectrometer at Triumf and its associated BGO γ‐array. For the first time the full level scheme involved in this process has been measured and shows previously unobserved γ‐decay to doorway states around 11 MeV in 28Si.

We extend the classical Landau theory for rotating nuclei and show that the backbending in 162Yb, that comes about as a result of the two-quasiparticle alignment, is identified with the second order phase transition. We found that the backbending in 156Dy, caused by the instability of $\gamma$-vibrations in the rotating frame, corresponds to the first order phase transition., Comment: 4 pages, 2 figures

Thermal neutron capture gamma-ray spectra for {sup 187}Re(n,{gamma}){sup 188}Re reaction were measured. Singles and coincidence spectra were detected in order to develop the level scheme. The evaluation is in progress, of which the first results are obtained from the analysis of coincidence spectra, allowing to check the level scheme below 500 keV excitation energy. Seven low-energy negative parity bands are developed in order to find better energies for rotational levels. With a good confidence, a few positive parity bands are developed as well. Rotor plus two quasiparticle model calculations, employing effective matrix element method are performed for the system of six negative parity rotational bands.

High quality radioactive beams have recently made possible the measurement of (d,p) reactions on unstable nuclei in inverse kinematics, which can yield information on the development of single-neutron structure away from stability, and are of astrophysical interest due to the proximity to suggested r-process paths. The Oak Ridge Rutgers University Barrel Array (ORRUBA) is a new high solid-angular coverage array, composed of two rings of silicon detectors, optimized for measuring (d,p) reactions. A partial implementation has been used to measure (d,p) reactions on nuclei around the N = 82 shell closure.

New measured differential cross sections of tritons and alpha particles following the 6Li(n,t)α reaction are reported for incident neutron energies between 0.2 and approximately 20 MeV. The neutrons were produced by spallation at the WNR facility at the Los Alamos Neutron Science CEnter (LANSCE), with the incident neutron energy determined by the time‐of‐flight method. Four E‐ΔE telescopes were used at eight laboratory angles. These data have been incorporated into a prior R‐matrix fit for the compound 7Li system, and result in an (n,t) reaction cross section that is 4% to 10% higher than previous evaluations in the 1–3 MeV incident neutron energy region.

Existing experimental data on γ decay of energy levels in medium‐weight and heavy nuclei at excitation energies well above the pairing gap indicate that the role of nuclear structure effects is small and that this decay is largely governed by the extreme statistical model. Specifically, in line with the validity of Brink hypothesis and the paradigm of photon strength, the average properties of the γ decay can be described by a set of photon strength functions (PSFs) for individual multipolarities and by the level density function. PSFs are directly related to the photoabsorption cross sections σγ abs. It is well known that in the case of E1 radiation this cross section is dominated by the giant dipole electric resonance. However the size of σγ abs. and its γ‐ray energy dependence at energies below the neutron threshold are known rather poorly. In the case of higher multipolarities (M1, E2,…) the present knowledge about their roles is much worse. Available information on E1 and M1 PSFs obtained from variou...

Starting from an effective Skyrme interaction we present the finite rank separable approach for the quasiparticle random phase approximation. The approach is generalized to take into account the residual particle‐particle interaction. As an illustration of the method properties of the low‐lying quadrupole states in the even‐even nuclei around 132Sn are studied.

By using an empirical power law function with two fit parameters, the multiplet splitting for more than 30 pure particle‐hole states (with values between −0.3 and +0.6 MeV) is described with a residual energy difference of about 0.03 MeV.

A search for an anomalous n‐p scattering from a polyethylene sample (CH2) at 8 final energies between 64 eV and 2.5 keV was carried out. The scattering intensities were compared to that from a graphite (C) sample. The results were found to confirm our previous n‐p results on H2O at a final energy of 24.3 keV where no n‐p scattering anomaly was observed. The present results refute all proposed models attempting to explain the occurrence of any n‐p scattering anomaly at keV neutron energies.

We present evidence of the existence of a new supersymmetric quartet of nuclei in the A=190 mass region. The analysis is based on new experimental information on the odd-odd nucleus 194Ir from transfer and capture reactions. The new data allow the identification of a new supersymmetric quartet, consisting of the 192,193Os and 193,194Ir nuclei. We make explicit predictions fo r193Os, and suggest that its spectroscopic properties be measured in dedicated experiments. Finally, we study correlations between different transfer reactions.

The advantages of using inelastic neutron scattering with detection of the emitted γ rays, i.e., the (n,n′γ) reaction, for exploring the structure of stable nuclei are reviewed. Examples of the information available with these techniques are provided and progress in understanding multiphonon excitations is described. The unique nuclear structure of 94Zr is discussed.

Positron‐electron pair creation near the threshold energy is extremely difficult to investigate by both experiments and theory. First test experiments were performed at the ILL to determine the cross sections for positron‐electron pair creation near threshold using prompt γ‐rays from different targets after neutron capture and conventional radioactive sources. Pair creation was studied in a Ge detector, which simultaneously acted as sample and detector. First results are presented which show a significant deviation from theoretical values near threshold.

An improved extrapolation method for shell model calculations is presented. By axially symmetric bases, computation is drastically simplified.

Understanding the origin, structure, and phases of hadronic matter is a forefront research area in physics. An integral part of this challenge is to achieve realistic modeling of the complex dynamics of atomic nuclei, which is key to comprehending the evolution of the universe from a fundamental quark/gluon level. We recently demonstrated the potential power of an innovative concept, the ab initio symplectic no‐core shell model (Sp‐NCSM), based on expanding the conventional harmonic oscillator basis in terms of the symmetry‐adapted and physically relevant symplectic basis, to reach new domains of nuclear structure. Using realistic interactions tied to Quantum Chromo‐dynamics (QCD), the Sp‐NCSM approach holds promise to build the bridge from QCD to measured properties of light nuclei, predict diverse features of unstable nuclei crucial for astrophysical processes, and provide nuclear structure information essential for cosmology and probing physics beyond the standard model.

Multipole mixing ratios for transitions between excited 2+ states and the 21+ state in 140Nd are measured using angular correlation techniques for beta decay reactions. Two transitions with dominant M1 components are identified, and the higher‐lying 2+ states involved in these transitions are presented as candidates for the one‐phonon mixed‐symmetric 2+ state in 140Nd. Assuming pure two‐state mixing between the one‐phonon 2+ state and a presumed three‐phonon symmetric state yields a mixing matrix element between these states, which is discussed in terms of shell effects on mixed‐symmetric behavior in the N = 80 isotones.

Lifetimes and g‐factors have been measured for short‐lived low‐lying states in 70Zn using the techniques of projectile Coulomb excitation in inverse kinematics combined with transient magnetic fields and the Doppler‐Shift‐Attenuation‐Method (DSAM). While the g(21+) value was redetermined and found to be consistent with the literature values, all other data are new. The main goal is a better understanding of the influence of the v(g9/2) orbital in this region of the nuclear chart.

This conference paper outlines the operation and some of the preliminary physics results using the GSI RISING active stopper. Data are presented from an experiment using combined isomer and beta‐delayed gamma‐ray spectroscopy to study low‐lying spectral and decay properties of heavy‐neutron‐rich nuclei around A∼190 produced following the relativistic projectile fragmentation of 208Pb primary beam. The response of the RISING active stopper detector is demonstrated for both the implantation of heavy secondary fragments and in‐situ decay of beta‐particles. Beta‐delayed gamma‐ray spectroscopy following decays of the neutron‐rich nucleus 194Re is presented to demonstrate the experimental performance of the set‐up. The resulting information inferred from excited states in the W and Os daughter nuclei is compared with results from Skyrme Hartree‐Fock predictions of the evolution of nuclear shape.

We propose an approach to nuclear pairing at finite temperature and angular momentum. This approach includes the effects due to the quasiparticle‐number fluctuation and dynamic coupling to pair vibrations within the self‐consistent quasiparticle random‐phase approximation. The pairing gaps, total energies, and heat capacities are calculated within a doubly folded multilevel model as well as several realistic nuclei. The results obtained show that, in the region of moderate and strong couplings, the sharp transition between the superconducting and normal phases is smoothed out. This is manifested in a thermal pairing gap, which does not collapse at a critical temperature predicted by the conventional Bardeen‐Cooper‐Schrieffer’s (BCS) theory, but has a tail extended to high temperatures. Moreover, this approach also predicts the appearance of a thermally assisted pairing at finite angular momentum. The effect of backbending of the momentum of inertia as a function of the square of angular velocity is also discussed.

We study the structure of isomeric state 21+ in the odd‐odd N = Z nucleus 94Ag using a shell model, which is capable of describing the spectra of upper g9/2‐shell nuclei close to the N = Z line. It is shown that the 21+ state becomes isomeric because of level inversion of the 19+ and 21+ states due to core excitations across the N = Z = 50 shell gap. Calculation of spectroscopic quadrupole moment indicates clearly an enhancement in these states due to the core excitations. In the present shell model calculation, however, the large‐deformation picture of Mukha et al. in Nature 439, 298 (2006) cannot be accepted.

Using the HORUS spectrometer at the Cologne FN‐TANDEM accelerator, we performed a γγ coincidence measurement on 88Zr. The reaction used was 89Y(p,2n)88Zr. A particular point of interest was the search for a potential 2+ mixed‐symmetric state. In the experiment, we measured the multipole mixing ratios of the decays of the 22+ and the 23+ states and determined the energies of the 23+ and 02+ states precisely. Furthermore, we found two new levels and seven new γ transitions.

We propose a novel way of determining the Hamiltonian of the Interacting Boson Model (IBM), based on the Mean‐field theory. The quadrupole deformations in a fermion system, indicated by a Potential Energy Surface (PES) obtained by the constrained Skyrme Hartree‐Fock calculations, are mapped, to a good approximation, onto the appropriate boson system. A merit is that levels and wave functions of excited states are calculated with the exact treatments of angular momentum and particle number. The validity of the process is examined for Sm and Ba isotopes, and predictions are made for unexplored territories on the nuclear chart, namely the right‐lower corner of 208Pb.

For fissile actinide targets 233U, 235U and 239Pu the capture cross sections are strongly influenced by the target spin, fission transition states spectroscopy and fission/γ‐emission competition of the compound nuclides. The capture cross sections were obtained via a consistent description of fission and elastic/inelastic scattering, (n,γf) reaction being included.For neutron capture reactions on even‐even U, Pu and Cm nuclei the methods, proven in case of 232Th(n,γ) and 238U(n,γ) data analysis are used. Calculated 240Pu(n,γ) and 244Cm(n,γ) reaction cross sections shapes are much similar to that, observed for the 238U(n,γ) and 232Th(n,γ) reactions. Differences are due to fission and neutron emission competition, which depends on the (Z,N)‐composition of the compound nucleus.

The neutron time‐of‐flight facility GELINA installed at the IRMM Geel (B) has been designed to study neutron‐induced reactions in the resonance region. It is a multi‐user facility, providing a pulsed white neutron source, with a neutron energy range between 10 meV and 20 MeV and a time resolution of 1 ns. The research program concentrates on cross section data needs for nuclear energy applications. In this paper efforts to improve the quality of cross section data for neutron induced capture reactions in the resolved and unresolved resonance region are presented together with examples of cross section data to support the development of advanced reactor concepts and to optimize the use of present nuclear power plants.

International audience; We use a new approach based on image reconstruction techniques to improve model-based predictions of nuclear masses. A partial view image pattern is built by taking the differences between experimentally measured masses and the predictions given by different theoretical models which describe the smooth macroscopic behavior. We show that it is possible to significantly improve predictions in regions not too far from measured nuclear masses.